Surface osteosarcoma: Predictors of outcomes.

BACKGROUND AND OBJECTIVES: The subtypes of surface osteosarcomas include well-differentiated, low-grade parosteal osteosarcoma (POS), intermediate-grade periosteal osteosarcoma (PerOS), high-grade surface osteosarcoma (HGSO), and high-grade, dedifferentiated POS (dPOS). We aimed to determine disease progression, defined as local recurrence and metastatic disease, and overall (OS) and disease-specific survival (DSS). We identify outcome predictive factors and report functional results.

METHODS: This retrospective study evaluated patients with primary surface osteosarcoma at our hospital from 1992 to 2019. Fifty-one patients had a median follow-up of 6.1 years (range: 0.1-25.2). Histologic subtypes included 32 POS, 11 PerOS, 4 HGSO, and 3 dPOS. Bone and soft tissue margins were classified using the American Joint Committee on Cancer residual tumor classification (Rx = Not evaluable; R0 = negative margin; R1 = microscopic positive margin; and R2 = macroscopic positive margin) and the modified R classification (mRx = not evaluable; mR0 = negative margin >1 mm; mR1 = negative margin ≤1 mm; mR1-dir: Positive microscopic margin locally; mR2a: Positive macroscopic margin locally; mR2b: positive macroscopic margin distally; and mR2C: positive macroscopic margin locally and distally). Forty-one patients had functional outcomes.

RESULTS: Three POS patients developed recurrence: two had R0 margins and one an intralesional resection. Five patients developed lung metastases (POS: 3, dPOS: 2). Four patients died. The only significant disease progression predictor was age. OS at 10 years was 97%. 48 patients had negative bone margins (R0 or mR0 and mR1) and 47 patients had negative soft-tissue margins (R0 or mR0 and mR1). The average MSTS score was 88.43 (range: 34.29-100).

CONCLUSIONS: We advocate surgery for POS and believe R0 (mR0 and mR1 resections) or planned R1 (mR1-dir) to preserve function are acceptable. We favor chemotherapy and surgery for PerOS, though a chemotherapeutic response is highly variable. High-grade tumors are the most infrequent subtype, but HGSO and dPOS seem to portend a poorer prognosis. Good function can be obtained.